The history of the bicycle goes back many years. A crude two-wheeled vehicle propelled by the feet was popular as early as the second half of the 17th century. Extensive developments to the design of the bicycle were made during the 19th century. At the end of the 19th century, the bicycle had become a serious means of transportation. In 1899, the U.S. production of about 1,000,000 bicycles a year was valued at $31,000,000. However, by 1909 the bicycle industry in the U.S. was nearly nonexistent due to the advent of the motorcycle and automobile. Bicycle riding was generally confined to children and to small groups of devotees, such as members of the League of American Wheelmen, organized in 1880 and the Century Road Club Association, organized in 1899.
It was not until the 1960""s and 1970""s and more recently in the 1990""s that bicycling once again began to enjoy strong popularity. There are several modem reasons that may have resulted in this strong resurgence. Air pollution, traffic congestion, and the high cost of automobile fuel are all reasons that it makes sense to use a bicycle for transportation. Personal fitness is also a modem trend that is very popular. The bicycle is an outstanding device to use for physical exercise.
As the bicycle has developed and has become firmly established as part of our modem culture, its use has expanded in recent years. For example, in addition to the traditional road bicycle, mountain bikes and BMX bikes are now very popular.
As bicycle frame technology has improved, bicycle designers have focused on making bicycle frames that are lightweight and strong. Similarly, bicycle designers are concerned about building bicycle frames in a cost effective and time efficient manner. Monocoque bicycle frames are extremely popular for road, mountain, and BMX bicycles. A monocoque structure is one in which the skin absorbs all or most of the stresses to which the structure is subjected.
There are two common methods for making a hollow monocoque bicycle frame. The first method is by extruding individual hollow tubular frame sections. These frame sections can then be cut to length, bent to a desired shape, coped, aligned and then individually welded together to produce a bicycle frame. Some of the major disadvantages to making bicycle frames in this manner are: 1) the manufacturer is limited by available extruded tubing material and sizes, 2) the thickness and cross section of the tube cannot vary with stress, 3) the amount and type of bending and coping that he is able to do to the extruded frame sections, and 4) the extra time it takes to individually align and weld each frame member together, and 5) the time necessary to align each frame after welding.
The second known method involves forming matching frame half-shells and then welding them together along their entire seam. The advantage of the second method over the first is that the cross sectional area of the welded frame sections can vary along their length. However, welding formed matching half-shells along their entire seam is a time consuming and complicated process. Because welding a bicycle frame is considered to be delicate work, welders have to be highly trained or high cost robotic welders are used to do an effective, consistent and esthetically acceptable job. Therefore, it is much more expensive to weld formed matching half-shells together than it is to extrude individual frame sections and then weld those together.
Brazing is a method of joining together metals by inserting the entire work into a hot volume (such as a molten salt bath or a hot furnace) and using a filler metal with a melting point lower than that of the metals to be joined. Brazing is well known in the prior art.
What is needed is a more efficient method for making monocoque bicycle frames.
The present invention provides a brazed bicycle frame and method for making. At least two bicycle frame half-shells are fabricated. A filler metal is then placed between the bicycle frame half-shells to form a two-part hollow frame section. The two-part hollow frame section is inserted into a hot volume at a temperature higher than the melting temperature of the filler metal but lower than the melting temperature of the two bicycle frame half-shells. The filler metal is allowed to melt. The filler metal is then allowed to cool and harden to form a rigid joint. In one preferred embodiment the bicycle frame half-shells each have a flange that facilitates alignment fixturing and assembly of the two-part hollow frame sections. In another preferred embodiment the filler metal and the bicycle frame half-shells are placed in an extruded or formed grooved section. The grooved section also facilitates alignment fixturing and assembly of the two part hollow frame sections, and helps to strengthens the braze joint.